Transaction fees for transfering BITCOINS  -- WTF

I have been testing transfering BITCOINS from web based to my wallet client. However I have noticed that if I try to transfer from my wallet client to a web based site the local wallet client prompts me for a "Transaction fees"

WTF... i understood the concept behind BITCOIN was FREE. 

CAN someone explain on a BASIC LEVEL... i do not need buzz words in the explain. why a fee

How do I have my graphic card make and model   (ie. windows xp "mycomputer" properties) 

For;
windows xp
or
window 7

I am new to all this, my question is does my computer going into PowerSaver or Screen off impact bitcoin pool mining ?

Does my computer running 24/7 increase the change my computer may crash. Burnout ??

thanks